Raising Uninterruptable Power Supply Efficiency with Eco mode

Recent UPS News publication, indicate that most new UPS systems emphasize the high
efficiency gained with Economy (called also Eco or High Efficiency) mode of operation. In
some cases manufacturers refer in press releases only to the high efficient Economy mode,
without even mentioning normal dual conversion mode of operation.

Latest Three phase UPS, offer both Double Conversion mode and Eco mode operation , for
instance: :

APC introduces MGE 7000 Galaxy 250 to 500 kVA UPS series with 97% efficiency in Eco
mode and 94.5% in double conversion mode.

Chloride introduces MP-.Net 20 to 80kVA UPS with 98% efficiency in Eco Mode and 94.5%
in double conversion mode.

Eaton introduces 9390IT 40kVA UPS with 99% efficiency in Eco Mode and 94% in double
conversion mode.

Socomec introduces Green Power 100kVA to 200kVA UPS with 98% in Eco Mode and 96%
in Double Conversion mode.

These examples refer only to systems introduced in the last few months. Eco mode operation
is offered for quire a time, by these and other manufacturers as well. GE for instance, has
thousands of units with Eco mode in the field today.

ECO mode operation is practically an Off Line operation with an On Line system. The load, if
this mode is selected, like with any Off Line UPS, is fed continuously from the mains,
transferred to UPS in case of utility failure or its deviation beyond set limits.

There is however a big difference between the Off Line and Online system types. An Off line
UPS system MUST work continuously from mains using the battery backup mode for short
backup times, while an Online system can work continuously in both modes.

An Off line UPS, in an unstable grid environment with frequent power excursions or outages,
will exercise frequent transfers from mains to battery operation. The critical load will be
exposed to mains transients and possible failure if unsmooth or unsuccessful transfer to the
battery occurs. Numerous battery discharges will short drastically battery life time.

Online UPS in a similar environment will behave similarly if set to Eco mode. But here, most
of the described hazards can be avoided by selecting the Double Conversion mode with
unstable grid environment. Some UPS systems will automatically change the working regime
to Online operation, even if Eco mode is selected, upon sensing unstable utility environment.

The gain in Eco mode is quite tempting. In average about 3.5% power saving is gained, just
considering UPS efficiency. Taking in account also cooling requirements, close to 9% of
output power can be spared. For instance, almost $6000 per year, about 17% of UPS cost,
can be saved by selecting Eco mode operation when working with 80% loaded 100kVA UPS.

Which operational mode to choose, depends on grid behavior and on the criticality of the
mission the UPS has to protect. Online, mode should be preferred in unstable grid situations,
regularly happening in certain seasons.

In stable grid environment, the cost of transfer malfunction from Eco mode to UPS mode, in
case of power failure should be evaluated before decision to select Eco mode is made.

The probability of such malfunction depends on local frequencies of mains failures, the
reliability of static switch (or static switches in parallel systems), and on the specific control
measures which ascertain that UPS's Online route, when on Eco mode, is healthy enough to
be sure that it won't let us down, when the lights go out.

Raising UPS Efficiency with Eco Mode